It has been well established that birth defects may be induced experimentally by heterologous antisera directed against certain tissue homogenates. The investigators isolated a glycoprotein from rat microvillar membrane and showed that rabbit antibodies to this glycoprotein antigen caused abnormal embryonic development. They are interested in the underlying mechanism whereby such specific antibodies can cause embryopathy. In order to delineate the mechanism of teratogenesis, the following projects will be performed: 1) production of monoclonal antibodies to the glycoprotein, 2) purification of aminopeptidase M from brush-border membrane, 3) identification of the antigenic peptides by protein blotting, 4) identification of the antigen by histochemical staining method, 5) studies of antigen distribution in various tissues by indirect immuno-peroxidase technique, 6) production of auto- or alloantibodies in pregnant rats, 7) ultrastructural localization of teratogenic IgG in vivo, 8) studies of ultrastructural changes in the visceral yolk-sac endoderm after teratogenic antibody administration, 9) studies of the effects of teratogenic IgG on visceral yolk-sac pinocytic uptake of macromolecules in vitro, 10) kinetic studies of immunoinhibition of aminopeptidase M activity and survival of visceral yolk-sac endodermal cells in culture, 11) studies of effects of teratogenic IgG on visceral yolk-sac release of N-acetylglucosaminidase and toxic oxygen metabolites, 12) studies of effects of teratogenic IgG on macrophage functions. The long-term objective of these proposed projects is to delineate the mechanism of teratogenesis induced by heterologous brush-border membrane antibodies.